This application is based upon and claims priority of Japanese Patent Application No. Hei 10-374594, filed the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetic hard disk capable of writing and reading magnetic data thereon, and more particularly, to a magnetic hard disk having concentric magnetic tracks spaced to each other on a non-magnetic substrate, and a fabrication method thereof.
2. Description of the Related Art
As the infrastructure of information and communication in the society is progressed, a magnetic hard disk driver (or HDD) as an external memory of computers rises in importance increasingly, and its storage density increases rapidly year by year. Tendency for seeking smaller size and larger volume in the memory demands narrower magnetic tracks and higher storage density for the magnetic hard disk.
Since storage density of the magnetic hard disk depends upon both of linear density along a track and track density in the radial direction, improvement of either one or both results in higher storage density of the magnetic hard disk. The present invention is directed to an improvement of a technology related to the track density.
In general, auxiliary data is initially recorded on a magnetic hard disk, which is information necessary for writing or reading data on the magnetic hard disk, such as servo data (or tracking servo data) for positioning a magnetic head on a track, address data for registering a position of written data and PLL lock data for reading out address data. To increase the track density, simply narrowing a space between tracks results in a serious problem under a circumstance that a track is generated by writing data by a magnetic head as in conventional manner. FIG. 1A is a partial cross-sectional view of a typical conventional magnetic hard disk having a continuous magnetic film, in which the magnetic disk consists of a flat substrate 1 and successively laminated three thin films of chromium 2, cobalt-chromium-platinum-tantalum alloy 3, and amorphous carbon 4. When narrow-pitched magnetic tracks are written on a continuous magnetic film by simply narrowing a spacing between magnetic head trajectories of the nearest neighbors, a stray magnetic field coming out laterally from both sides of the magnetic head magnetizes a guard band between tracks which resultantly causes magnetic noises. Narrowing track width also gives rise to decrease of a signal to noise ratio (or S/N) problem at reading out a written data. The similar problem occurs in recording of tracking servo data for controlling a position of a magnetic head. As narrowing the track width, it becomes increasingly difficult to obtain a highly accurate servo data. To maintain the S/N ratio for narrower track width, it has been proposed to form various physical features such as bumps or grooves on a surface of a disk substrate by which servo signal or position of a track is determined. (for instance, a Japanese Laid Open Patent Application H3-252922). According to this technique, a servo mark is formed on the magnetic disk for tracking a magnetic head by which the magnetic head can be controlled to follow a magnetic track with high accuracy. The servo mark is written by servo writer. Narrowing track width for higher track density requires higher accuracy in positioning the servo mark, which further needs higher positioning accuracy between a servo writer and a HDD. Therefore, a drawback of this approach is requirement for higher technical accuracy to the positioning device which incurs extra cost. To overcome this drawback, it has been proposed to pre-form the servo mark by which accuracy in positioning the servo mark can be increased. Several methods for pre-forming the servo mark are disclosed, for instance, by etching a magnetic film as in Japanese Laid Open Patent Applications S62-256225 and H1-23418, or by forming bumps and grooves on a disk substrate as in H8-17155. FIG. 1B is a partial cross-sectional view of another typical conventional magnetic hard disk having a partially refilled groove between magnetic tracks neighboring to each other, in which the magnetic disk consists of a flat substrate 1 and successively laminated three thin films of chromium 2, cobalt-chromium-platinum-tantalum alloy 3, and amorphous carbon 4, as same as FIG. 1A except that there are partially refilled grooves 7 between pre-determined tracks 8.
However, a drawback of these methods is to leave surface roughness from several tens nanometers to several hundreds nanometers in overall height on the magnetic disk. Since floating stability of a magnetic head, which means how stably a magnetic head can maintain a predetermined distance from the rotating magnetic disk, for a magnetic disk of high track density in a conventional HDD can be attained by flattening and smoothing the surface of a magnetic disk, and since decrease of the distance between a floating magnetic head and a magnetic disk is also needed to operate a magnetic disk having higher density maintaining the appropriate S/N ratio, the both approaches clearly conflicts with these technical requirements.
An object of the present invention is to provide a magnetic hard disk having a plurality of concentrically disposed magnetic tracks with high radial density, which maintains sufficiently long durability of a non-contact magnetic head floating immediately above the magnetic tracks, the magnetic hard disk comprising a non-magnetic substrate having an upper surface with a concentrically patterned magnetic film thereon, and a non-magnetic protecting film on the entire upper surface of the magnetic hard disk, wherein roughness of the upper surface of the non-magnetic protecting film is in a range between 0.5 nm and 3 nm.
Another object of the present invention is to provide a magnetic hard disk having high radial density of magnetic tracks without degrading signal to noise ratio. According to one aspect of the invention, a magnetic hard disk comprises a non-magnetic substrate having alternately disposed concentric banks and grooves on the upper surface, a magnetic film on each of the concentric banks, and a non-magnetic film covering the magnetic film and refilling the grooves such that the upper surface of the non-magnetic film has the same surface roughness and continuity across the banks and grooves.
Further object of the present invention is to provide a reliable method for fabricating the magnetic hard disk having high radial density of magnetic tracks, the method comprise the steps of forming alternately disposed concentric banks and grooves on a non-magnetic substrate, forming a magnetic film and a first non-magnetic film on each of the concentric banks, successively forming a second non-magnetic film on an entire surface of the magnetic hard disk so as to cover the first non-magnetic film and refill the grooves therewith, removing the second non-magnetic film from the upper surface of the first non-magnetic film by Damascene method until the first non-magnetic film is exposed, and subsequently forming a third non-magnetic film on an entire surface of the magnetic hard disk and finally roughening the upper surface of the third non-magnetic film such that roughness of the upper surface of the third non-magnetic film falls in a range between 0.5 nm and 3 nm.